This invention relates to a hoist apparatus and more particularly to an elevator gearless hoist apparatus.
FIG. 1 illustrates a general structure of an elevator system with a hoist apparatus, in which reference numeral 8 designates main rope, 9 an elevator car, 10 a counter weight, 2 an electric motor and 3 designates a sheave. The electric motor 2 and the sheave 3 are securely mounted on a base 1 which in turn is installed in machine room 11. The elevator car 9 and the counter weight 10 are connected through the main rope 8 wound around the sheave 3, so that when the sheave 3 is rotated by the motor 2, the main rope 8 is driven to move the elevator car 9 along the hoistway.
One example of the structure of a gearless elevator hoist apparatus comprising the electric motor 2 and the sheave 3 as disclosed in Japanese Patent Laid-Open No. 61-217486 is illustrated in FIG. 2. In FIG. 2, the base 1 is secured in the machine room 11 and the electric motor 2 is mounted on a pedestal or a support bracket 12 mounted to the base 1. Reference numeral 2a designates a rotary shaft of the electric motor 2, 6 is a hollow tubular shaft secured to the support bracket 12. The sheave 3 having rope grooves 3a around it for receiving the main ropes 8 therein is rotatably mounted on the hollow shaft 6 through a bearing 4. On the other hand, the sheave 3 is fixedly mounted on the motor rotary shaft 2a through a connecting plate 7. An electromagnetic brake unit 13 is mounted on the support bracket 12 so that its shoes are pressed against a brake drum 5 integrally formed on the sheave 3.
The rotation of the rotary shaft 2a of the electric motor 2 causes the sheave 3 to rotate through the connecting plate 7, whereby the main ropes 8 are driven to move the elevator car 9. The load on the sheave 3 is transmitted through the bearing 4 to the hollow shaft 6, and the load on the hollow shaft 6 is supported by the support bracket 12 and the base 1.
In the elevator hoist apparatus as above described, the sheave 3 is disposed in an axially aligned relationship with respect to the rotary shaft 2a of the electric motor 2, so that the axial dimension of the hoist apparatus is relatively large, imposing a dimensional limitation when the hoist apparatus is to be installed in the machine room 11. In order to meet this dimensional limitation, the axial dimension is decreased by increasing the radial dimensions of the electric motor 2 and the sheave 3. With this arrangement, since the diameter of the sheave is large, the connecting plate 7 as well as the hollow shaft 6 for transmitting the rotational force and supporting the load become large, thereby disadvantageously increasing the weight of the apparatus.
FIG. 3 illustrates one example of a hoist apparatus disclosed in Japanese Utility Model Laid-Open No. 52-32870 and proposed to overcome the above-discussed problems. In FIG. 3, the hoist apparatus comprises a stationary shaft 14 supported at opposite ends by a pair of support stands 17. The stationary shaft 14 securely supports thereon a motor stator assembly 16 including a stator iron core and a stator coil. The stationary shaft 14 rotatably supports a sheave 3 with rope grooves 3a through a pair of bearings 4. The sheave 3 has a substantially drum-shaped configuration having a substantially U-shaped cross section. A motor rotor assembly 15 including a rotor core and a rotor coil is firmly attached to the inner circumferential surface of the sheave 3. In this context, the sheave 3 also functions as a motor frame for supporting the motor rotor assembly 15.
In this hoist apparatus, the motor frame and the sheave are combined into a single common member, so that the axial length of the hoist apparatus is much shorter than that shown in FIG. 2, realizing a light-weight hoist apparatus. However, while the motor frame and the sheave are combined in this hoist apparatus, the opposite ends of the sheave 3 are supported through the pair of the bearings 4 on the stationary shaft 14 and this shaft 14 is supported at the portions outside of the bearings 4 by the support stands 17, so that the overall axial length of the hoist apparatus is still relatively long.
Generally, the operating life of the sheave significantly decreases as the diameter of the sheave is decreased due to the frictional wear between the rope grooves of the sheave and the main ropes. When a worn sheave is to be replaced with a new one, the firmly assembled sheave itself must be disassembled and then the motor rotor assembly and the motor stator assembly must also be dismounted from the sheave and the shaft, respectively, causing the exchange of the sheave to be very difficult. Accordingly, it has been practiced that the sheave is designed to have an operating life three or four times longer than that of the main rope, thus decreasing the frequency of the need for the sheave exchange. However, with a small-diameter sheave, the wear of the sheave and the main rope is larger, so that a special material must be selected for the sheave, which makes the sheave expensive and a severer load is applied to the main rope, further shortening the life of the main rope and increasing the need for frequent maintenance.